Method of making cast magnetic aluminum-iron alloys and product thereof



United States Patent G METI-IQD OF MAKING CAST MAGNETIC ALUMI- NUM-IRQN ALLOYS AND PRODUCT THEREOF Robert D. Ahles, Schenectady, N. Y., assignor to General Electric Company, a corporation of N ew York No Drawing. Application January 30, 1953 Serial No. 334,353

Claims. or. 140-121 This invention relates to magnetic materials and more particularly to cast alloy magnets consisting essentially of iron alloyed with approximately 0.8 to 6.2 percent by weight, aluminum based on the weight of the total alloy, and having high permeability, with varying specific resistance, and very low hysteresis loss.

Magnetic materials consisting principally of iron with up to 10 percent content of aluminum are known. These alloys have been used as magnetic cores in various electrical machines and apparatus such as transformers, loading coils and the like. To obtain the desired magnetic properties, the known alloys have been subjected to a hot or cold rolling process by annealing with or without subsequent heat treatment.

The present invention is based on the discovery that iron-aluminum alloys having good magnetic properties can be obtained in the as-cast condition without any irons, there is obtained a maximum permeability of 18,000 at a flux density of about 8,700. The He and Br "figures are .27 to .30 oersted and 7,300 to 8,000 gauss,

respectively.

These heat-treated cast aluminum iron alloys present much better magnetic properties than any presently used cast iron-base material. For example, the better steel castings have permeabilities in the order of magnitude of 4,000 with values of He and Br of 2.5 to 3.0 oersteds and 7,000 to 8,000 gauss, respectively.

In producing the alloys of the present invention, the metals are melted and alloyed in any suitable apparatus as through the use of an induction furnace or the like. The molten mass may then be cast in a suitable .mold. Thereafter, it is heat-treated or annealed, the temperature of this operation depending on the aluminum content of the alloy. Thus, it has been determined that the optimum temperature is 900 C. for the 1 percent aluminum alloy, 950 C. for the 2 and 4 percent, and l,000 C. for the '6 percent material. The cooling rate, if it does not exceed 150 C. per hour, is not critical. It hasfurther been determined that heat treating from four to eight hours at the appropriate temperature will develop the optimum magnetic properties. Times much shorter or longer than this will in most cases either not develop, or will destroy, the optimum properties.

For the purpose of illustrating the improved properties of the instant heat-treated alloys and for purposes of comparison with other cast alloys, the following data is presented.

TABLE I Resis- Material Max. per- Intrinsic Hmmiea) Br 0 tivity meability saturation B=l5,000 B=10,000 B=10,000 microhm, cm./cm.?

Cast 1% Al-iron 20,000 20. 700 2. 5 8. 900 .30 2513 Cast 2% Al-iron 20, 000 20. 100 10. 0 8, 400 28 .36. 0 Cast 4% Al-iron 22, 750 19, 100 20. 0 8, 350 25 54.? Cast 6% Al-lron. 18,000 18, 100 55. 0 7. 400 24 70.6 Cast 3% C Steel 1,060 20, 300 45. 0 7, 500 3. 25 19. 0 Grey cast iron 385 16, 300 750.0 4, 750 6. 20 70-100 Ductile cast iro 1,675 10,900 150.0 6, 200 2. 3 7 60-80 Malleable iron 2, 100 18, 600 175. 0 .6, 350 1. 48 30-45 Cast 2% Siron 6,700 20,400 9.0 Cast 4% Siiron 4, 400 19, 300 '35. 0

Working by a'suitablelheattreatment of the cast material. As a result, it is possible to obtain magnetic products at a low cost through simple operations.

The alloys with which the present invention is concerned, as mentioned above, consist of a major proportion of iron and from 0.8 to 6.2 percent aluminum. The alloy should be substantially carbon-free and silicon-free, that is, it should contain a maximum of 0.35 percent silicon, a maximum of 0.05 percent carbon and only a trace of manganese at the most.

I have found especially good permeability at high flux densities in iron containing approximately l'to 6 percent aluminum. These properties are obtainable in the cast material-after a proper heat treatment. For example, 1 have found in the 1 percent aluminum iron maximum permeabilities of 20,000 at a flux density of 11,000 lines per square centimeter. The coercive forces Fla and residual magnetism Br are also low in this material; Hc being .3 to .36 oersted, with Br of 8900 to 9100 gauss,

Heat N0. 0 st Mn Al .Fe

0010 0.25 0.00 1.02 Bat, 0.028 0.27 0.03 1.09 Bal. 0.020 0. 23 0.04 4.00 Bal. 0.022 0.20 0.00 0.21 Bal.

Results of D.-C. normal-induction and hysteresis tests are shown in Table II.

TABLE II Magnetic and physical test results on heats 2169 through 2171 Heat N o. and Treatment Max. u at B B H H Sat. H B: B Br He H=100 B=l0,000 B=15,000 Intrinsic Bs-l-H B=10,000 B=10,000

2108A as cast.---- ,550 8, 550 17,900 2. 22 10. 800 20,500 21,300 8,200 1.14 2169A as cast. 5. 500 8, 000 ,200 1. 85 20. 0 800 20,000 20,800 7, 700 0. 72 2170A as cast 8, 425 5,000 16,700 1. 37 27.0 000 19,150 20,050 6, 000 0. 28 2171A as cast. 9,100 4, 500 16,000 3. 34 55. 0 800 18,100 18,900 4.200 0. 44 216813, 800 0 m 13,100 10,000 18,000 0. 81 2. 8 800 20,700 21,500 9, 050 0. 30 216815, 850" 0., 8 hrs., 19,250 11,000 18,000 0. 58 2. 3 800 20, 500 21,300 9,400 0.36 2168A, 900 0. 8 hrs line H 20, 250 11, 250 17,900 0. 56 2. 5 1,000 20.700 21,700 8, 900 0.30 21681 950 0., 8 hrs 1111c Hr 16,500 10.000 17,900 0. 56 4. 7 800 20,550 21,350 9,150 0. 38 21680, 1,000 0., 8 hrs lme H2 13, 200 11,750 17,900 0. 81 3. 3 1,000 20,500 21, 500 9,100 0.43 2168D, 1,100 0., 8 hrs., line 112.- 12,000 11,500 18,000 0. 81 3. 2 800 20,700 21,500 9,100 0.45 800 0 8 hrs .line 112.... 9,400 7, 500 17, 200 1. 04 9. 0 800 20.100 20,900 7, 950 0. 36 2109E, 850 0., 3 hrs., line H: ,200 7,000 17, 100 0.97 10.0 800 20,050 20,850 8,600 0. 34 216911, 900 0., 3 hrs. line 112-. ,300 10, 500 17, 300 0. 60 7.0 800 20,100 20,900 6, 950 0.19 21698, 950 0., 8 hrs, line Ha 20,000 10,000 17,200 0. 54 10.0 800 20,050 20,850 8, 400 0. 28 21690, 1.000 0 8 hrs line 114.- 17,000 10,250 .200 0. 56 8. 0 800 20,100 20,900 7,400 0.31 21090. l.l00 C 8 hrs line Hz" ,600 10,500 17,100 0.57 8.0 1,000 20, 150 21,150 6, 500 0.24 217013. 800 0., 8 hrs. line Hr 12,200 9,000 16,300 0. 88 39. 0 600 19.100 19,700 7,000 0.30 217019, 850 0., 8 hrs line H2" 800 9, 500 16. 400 0. 58 33. 0 800 19,150 19, 950 8, 300 0.30 217011 900 0., 8 hrs line H4 19,000 10,500 16,600 0. 53 24.0 800 19,100 19. 900 8,000 0.20 2l70F 950 0., 8 hrs 11110 112.... 2,750 11,000 ,900 0. 47 20. 0 800 19.100 19,900 8, 350 0. 21700, 1,000 0 8 hrs line Hz-- ,200 9, 500 16,300 0. 58 37. 0 800 19,200 20, 000 7, 250 0. 27 2170D, 1,100 0 8 hrs line H; 22, 750 9,750 16,400 0. 45 35. 0 600 19,100 19 700 8, 300 0. 26 217113, 800 0., 8 hrs line H2 10,100 7,000 16,100 1. 23 47, 0 600 18,100 18,700 6,750 0. 34 217113, 850 0., 8 hrs line H2" 11,400 6,000 16,100 1.15 47. 0 1,000 18, 200 19,200 6, 500 0. 30 2171A. 900 0. 8 hrs., line H2" ,400 9,750 16, 000 0.94 52. 0 800 18, 100 18,900 7, 300 0. 39 21718, 950 0., 8 hrs lino H2 17, 000 8, 750 16,200 0. 57 43. 0 600 18, 150 18,750 8, 000 0. 27 2171C, 1,000 C., 8 hrs., line Hz" 18,300 8, 750 15,900 0.66 55. 0 600 18,100 18,700 7, 400 0. 24 2171D, 1,100 0., 8 hrs., line Hz 18, 250 7, 250 15, 700 0.89 65. 0 600 18,150 18, 750 7,700 0- 24 Original 850 0., R-hours anneal gave very erratic and spotty results: therefore samples were reannealed for additional 4 hours at 850 C. These are the values reported. 850 0. seems to be the lowest critical temperature for treatment.

The resistivities of the l, 2, 4 and 6 percent aluminum alloys are 25.3, 36.0, 54.2 and 70.6 microhms per cm. respectively.

' From the results set forth in the'tables, it can be seen that, through proper heat treatment, a maximum permeability of 18,000 to 22,500 and good coercive forces are obtainable in the cast aluminum-iron alloys.

The physical properties of the cast and heat-treated aluminum alloys are also good; For example, the 1% aluminum alloy had a tensile strength of 36,000 p. s. i. with a 32% elongation while the 6% alloy had a tensile strength of 62,000 p. s. i. with a 17% elongation.

The present low Al-iron alloys can primarily be employed to replace high purity iron, such as Armco iron, which is now used for solenoid parts, cores, magnetic frames, etc. The 6 percent material which has a rela-- tively high resistivity may also be used in magnetic ap-' plications where laminated cores have formerly been used.-

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Substantially carbonand silicon-free magnetic allo cast articles consisting essentially of 0.8 and 6.2 percent aluminum, a maximum of 0.05 percent carbon, a maximum of 0.35 percent silicon and the remainder iron, prepared by casting the said alloys and subsequently heat treating said cast alloy articles without working said articles at about 900 C. to 1000 C. for a period of four to eight hours.

2. The method of obtaining good magnetic properties in cast substantially carbonand silicon-free magnetic alloys consisting essentially of 0.8 to 6.2 percent aluminum, a maximum of 0.05 percent carbon, a maximum of 0.35 percent silicon and the remainder iron, which consists of the steps of casting the alloy and then subjecting the cast alloy to a heat treatment of about 900 to 1000" C. for a period of four to eight hours.

3. The method of obtaining good magnetic properties in a cast substantially carbonand silicon-free magnetic alloy consistmg essentially of approximately one percent aluminum, a maximum of 0.05 percent carbon, a maximum of 0.35 percent silicon and the remainder iron, which consists of the steps of casting the alloy and then subjecting the cast alloy to a heat treatment of about 900 C. for a period of four to'eight hours.

4. The method of obtaining good magnetic properties in a cast substantially carbonand silicon-free magnetic alloy consisting essentially of approximately two percent aluminum, a maximum of 0.05 percent carbon, a maximum of 0.35 percent silicon and the remainder iron, which consists of the steps of casting the alloy and then subjecting the cast alloy to a heat treatment of about 950 C. for four to eight hours.

5. The method of obtaining good magnetic properties in a cast substantially carbonand silicon-free magnetic alloy consisting essentially of approximately four percent aluminum, a maximum of 0.05 percent carbon, a maximum of 0.35 percent silicon and the balance iron, which consists of the steps of casting the alloy and then subjecting the cast alloy to a heat treatment of about 950 C. for four to eight hours.

6. The method of obtaining good magnetic properties in a cast substantially carbonand silicon-free magnetic alloy consisting essentially of six percent aluminum, a maximum of 0.05 percent carbon, a maximum of 0.35 percent silicon and the balance iron, which consists of the steps of casting the alloy and then subjecting the cast alloy to a heat treatment of about 1000 C. for four to eight hours.

References Cited in the file of this patent FOREIGN PATENTS Switzerland Feb. 15, 1947 OTHER REFERENCES 

2. THE METHOD OF OBTAINING GOO<D MAGNETIC PROPERTIES IN CAST SUBSTANTIALLY CARBON- AND SILCION-FREE MAGNETIC ALLOYS CONSISTING ESSENTIALLY OF 0.8 TO 6.2 PERCENT ALLUMINUM, A MAXIMUM OF 0.05 PERCENT CARBON, A MAXIMUM OF 0.35 PERCENT SILICON AND THE REMAINDER IRON, WHICH CONSISTS OF THE STEPS OF CASTING THE ALLOY AND THEN SUBJECTING THE CAST ALLOY TO A HEAT TREATMENT OF ABOUT 900* TO 1000*C. FOR A PERIOD OF FOUR TO EIGHT HOURS. 